Various known spray guns have been developed for the purpose of reducing pressure losses between the air inlet and air outlet of guns. Conventional spray guns, high volume-low pressure (HVLP) guns and low volume-low pressure (LVLP) guns all suffer from a reduction in air pressure through the gun. In some instances, this reduction can be over 80%.
HVLP guns require very large volumes of air to maintain an acceptable atomization of the spray material. For example, to pass large volumes of air through an HVLP gun requires very high pressures to maintain a 10 psi (0.69 bar) pressure in the head of the gun, resulting in an average air consumption rate of approximately 20 scfm (566 l/min). With an input pressure of 75 psi (5.1 bar), the air expands on leaving the gun to regain its pre-compression volume. This will result in the atomized spray material being taken in all directions by the expanding air, in spite of the exit pressure being only 10 psi (0.69 bar). Thus, the spray output of HVLP guns can prove difficult to control.
Despite having a smaller clearance between the fluid tip and air cap than in HVLP guns, LVLP guns also suffer from pressure loss within the gun body. As a result, LVLP guns still require a high inlet pressure of 50–60 psi (3.45–4.14 bar) to operate at an atomizing (outlet) pressure of 15–18 psi (1.03–1.24 bar). Air consumption rates of LVLP guns range from 14–18 scfm (396–510 l/min), thus illustrating that LVLP guns are almost as inefficient as HVLP guns.
The main cause of the aforementioned inefficiency of HVLP and LVLP guns is the arrangement of the air passages within the gun body. The design and layout of air passages in the known guns leads to poor internal air flow efficiency.
It is therefore the aim of the present invention to provide a spraying apparatus which has a significantly improved air flow efficiency over known spray guns.